[ece]

There is nothing stopping Google or Facebook from offering content-based advertising to advertisers, publishers and users--sidestepping any issues with multiple small ad deals. A regulator could demand it if they wanted, and together publishers and advertisers could too. Individual users just don't have the same power, and resort to adblockers--which is pretty much their only option if they don't want to be tracked when a site doesn't have a subscription option.

[TravisLS]

Fair point. If you prohibit everyone, including walled gardens, from targeting based on user behavior or user data, that seems like a plausible solution.

It's a purely regulatory solution, though, not technical as the top level comment suggested :)

[ece]

Opt-in user targeting could still be fine (like offline loyalty programs), and it would be healthier than the current norm of opt-out through ad-blockers.